Variable resistor



May 27, 1969 L. GINSBERG 3,446,085

VARIABLE RES I STOR Filed March 24, 1967 Sheet of 2 ATTORNEYS y 1969 1.. GINSBERG 3,446,085

. VARIABLE RESISTOR Filedh'larch24, 1967 Sheet 2 of2 FIG. 3

ATTORNEYS United States Patent 3,446,085 VARIABLE RESISTOR Leon Ginsberg, Weston, Ontario, Canada, assignor to Precision Electronic Components Ltd., Toronto, Ontario, Canada, a company Filed Mar. 24, 1967, Ser. No. 626,374 Int. Cl. F16h 27/02 US. Cl. 7489.14 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to variable resistors or potentiometers and in particular to rotary variable resistors or potentiometers in which means are provided to prevent damage to internal components in the event of excessive rotation of actuating elements.

Background of the invention Variable resistors or potentiometers of the general type with which the present invention is concerned are not broadly new and have existed in various forms, for some time. A problem in the construction of devices of this kind which is common to most types, is the need to provide for some mechanism by means of which excessive rotation of the actuating element can be accommodated without damage to the internal components moved thereby. A number of arrangements and constructions have been proposed by the prior art with varying degrees of success. In general, those proposals of the prior art which have resulted in a substantially positive engagement between relatively movable parts have been subjected to the disadvantage that prolonged use produces excessive wear; those devices in which excessive wear is reduced have suffered from the disadvantage that their action is not positive and is subject to uncertainties and to a lack of precision.

Summary of the invention In the light of the deficiencies of, and difficulties encounted by the prior art, the present invention proposes a construction and arrangement of components by means of which a positive gear-type drive can be employed while, at the same time, providing the components with a construction to enable damage to be avoided in the event that the actuating element is excessively rotated in a direction tending to move the components beyond their normal limits of movement.

It is an object of the present invention to provide such a construction and arrangement which embodies a minimum number of parts and which parts are themselves simple in construction and operation and efficient over prolonged periods of use.

Further, the present invention provides for a construction which simplifies certain components, enables economies to be introduced both in manufacture and assembly and which, in general produces a device of high standards of quality, performance and precision.

Brief description of the drawings 3,446,085 Patented May 27, 1969 FIGURE 2 is a plan view of a portion of the assembled device of FIGURE 1 to illustrate a detail of construction and operation, and

FIGURE 3 is a view similar to FIGURE 2 showing the same components at a slightly later stage of operation.

Referring now to FIGURE 1, the variable resistor or potentiometer of the present invention may be seen to comprise a housing 10 which consists of a bottom wall 11, a first pair of side walls 12 and a second pair of side walls 13 which define an internal cavity 14 which may be closed by the application, to the housing 10, of a cover 15. The cover 15 comprises an upper planar element 16 having outside dimensions equal to the outside dimensions of the housing 10 and provided with an insert portion 17 having dimensions such that it will fit within the cavity 14 defined by the pairs of walls 12 and 13.

The insert portion 17 of the cover 15 is centrally recessed so as to receive an insulating wafer 18 (preferably ceramic) which, in turn, embodies a resistance track 19 and a collector track 20 exposed upon that surface of the wafer 18 which will be presented to the interior of the cavity 14 when the cover 15 is applied to the housing 10. Electrical contacts 21 extend through the cover 15 and the wafer 18 to make electrical connection with the resistance track 19 and the collector track 20 in a known manner to enable these components to be externally connected to whatever electrical circuitry is to embody the finished device.

7 The housing 10 and cover 15 will, preferably, be moulded from plastic material of appropriate physical and electrical characteristics and the wafer 18 which is preferably of ceramic material will normally be cemented in position by an appropriate adhesive.

One wall 13 of the housing .10 is provided with an aperture or bore 22 through which one end 23 of a shaft 24 carrying a worm gear 25 may project. The shaft 24 is provided with an enlarged collar 26 spaced from the slotted end 23 and an O-ring seal 27 is adapted to be received about the end 23 of shaft 24 so as to bear against collar 26. After the O-ring 27 has been received about the end 23 of the shaft and bears against the collar 26, the end 23 of the shaft is inserted into the bore 22 from inside the cavity 14 and moved so that end 28 of shaft 24 is resting in and is supported by a substantially semicylindrical recess 29 provided within the cavity 14 of the housing 10. The portion of the wall 11 of the housing 10 in the vicinity of the area occupied by the shaft 24 is moulded in such a manner as to provide appropriate contours to accommodate the configuration of the shaft 24 and its associated collar 26 and worm gear 25.

Since it is necessary that the cavity 14 be hermetically sealed means are provided to urge the shaft 24 in a direction tending to place the O-ring under compression between the collar 26 and the wall 13 of the housing 10. This means is embodied in a resilient block 30 of suitable material (e.g. hard rubber) filling in a recess 31 formed in the bottom wall 11 of the housing. The dimensions of the block 30, in a direction parallel to the axis of shaft 24 are such as to urge the shaft in a direction tending to compress the O-ring so as to provide a seal around the bore 22. The block 30 is of a height such that the insert portion 17 of the cover 15 will retain it in its recess 31 when the cover 15 is in position on the housing 10.

. The bottom wall 11 of the housing 10 is also provided with a centrally located, U-shaped recess opening into the moulded contour which is adapted to receive the shaft 24. This U-shaped recess 35 is provided with an upwardly extending, centrally located, cylindrical spindle or shaft 36 and the bottom Wall 37 of the U-shaped recess 35 is provided with a groove or slot 38 moulded therein which lies on a circular arc of less than 360,

the two ends of the arcuate slot 38 being spaced from one another at a point within the recess 35 remote from the location of the shaft 24.

A gear element 40 is provided having a diameter such that it can be received within the recess 35 and having a central, cylindrical socket or recess '41 which will fit over the spindle or shaft 36, thereby mounting the gear for rotation within the recess 35. The location of the shaft or spindle 36 is such that the gear teeth 42 of the gear 40 are firmly engaged with the worm gear 25 carried by the shaft 24 when both the shaft 24 and gear 40 are in their operative positions. The shaft 24, the collar 26 and the gear 25 will normally be formed from. metal while the gear 40 will normally be moulded from a plastic composition. The plastic composition itself provides certain inherent resiliency in the gear 40 and, accordingly, a quite tight or snug fit between the gear 40 and the gear 25 is contemplated, thereby reducing backlash between these two gears to a minimum.

The lower surface of the gear 40 is provided with a downwardly extending pin 43 which is received within the slot 38 and which, therefore, constitutes a stop, limiting the extend to which the gear 40 may rotate about the spindle '36 to that portion of a circular arc which is defined by the arcuate slot 38. Engagement of the pin 43 with either of the two ends 38a or 38b or the slot 38 will cause the gear 40 to cease its rotation regardless of the continued rotation of the worm gear 25 carried by the shaft 24. Since the shaft 24 may be continuously rotated (e.g. by a screwdriver engaged with slot 34) and since in the assembled device, it is impossible to visually determine the relative positions of the movable parts, means must be provided to ensure that this continued rotation of the worm gear 25 will not result in damage to the gear 40. This provision has been achieved by forming the gear 40 with an interrupted periphery at 44 and by removing material radially inwardly of the toothed periphery along an arcuate path indicated generally at 45. The effect of this removal of material is to provide the gear 40 with a pair of externally toothed, arcuate limbs 46 and 47 which, being radially unsupported at their extremities, are inherently resilient and flexible due to the characteristics of the material from which the gear 40 is made. The thickness of the limbs 46 and 47 is such that, under normal circumstances, the teeth 42 of the gear 40 will remain continuously in firm engagement with the worm gear 25 so that, throughout its limit of travel, the gear 40 will positively be rotated by any rotation of the shaft 24.

However, when the pin 41 engages one end or the other of the arcuate slot 38 and forces the gear 40 to cease in its rotation about its spindle 36, the conditions illustrated in FIGURES 2 and 3 will then apply.

In FIGURE 2, it can be seen that the pin 41 has come into contact with end 38a of slot 38 and that the gear 40 is, accordingly, in one limiting position and that further rotation of the gear in a counterclockwise direction (as seen in FIGURE 2) is no longer possible. It is possible, however, to continue the rotation of the shaft 24 and of the worm gear 25 and although this will tend to rotate gear 40, the flexible limb 47 provided by the present invention provides for an appropriate safeguard to prevent damage to the support.

Referring to FIGURES 2 and 3 it can be seen that continued rotation of the shaft 24 in the direction of the arrow 50 will, since gear 40 can no longer rotate, cause the flexible limb 47 to deflect radially inwardly and cause the teeth 42 of the flexible limb 47 to ride up upon the inclined surface of the engaging teeth of the worm gear 25 in a manner illustrated in FIGURE 3. Continued rotation of the shaft 24 will bring the crests of the engaging teeth of the worm gear 25 directly in opposition to the crests of the teeth 42 on the limb 47 and, further rotation, will enable the limb 47 to flex radially outwardly again so that its teeth 42 ride down the inclined surfaces of the teeth of the worm gear 25 so that they once again rest in 4 the trough of these teeth as shown in FIGURE 2. Continued rotation of the shaft 24 in this same direction indicated by the arrow 50 in FIGURES 2 and 3 will simply require the flexible limb 47 of the gear 40 to repeat the described process as often as is necessary.

Rotation of the shaft 24 in the reverse direction will immediately cause clockwise rotation of the gear 40 (as seen in FIGURES 2 and 3) and will move the pin 41 away from the end 38a of the slot 38. If rotation in this opposite direction is continued long enough, pin 41 will, eventually, engage end 3812 of the slot 38 and, in that event, limb 46 will perform the same ratcheting function relative to worm gear 25 as has been described with respect to limb 47.

Returning now to FIGURE 1, it can be seen that the upper face of gear 40 is provided with a central raised portion having a semi-cylindrical wall 51 terminating in a pair of radially inwardly extending walls or shoulders 52. A resilient metallic contact member indicated generally by reference character 53 is provided, the contact member having a first generally semi-circular edge 54 and a pair of opposed, toothed projections 55. A portion of the contact element 53 extends upwardly on a resilient arm 56 and terminates in a contact surface 57 which is intended to mechanically and electrically contact the collector track 20 carried by the wafer 18. A further upwardly curving and resilient arm 58 is provided terminating in a contact surface 59 which is adapted to mechanically and electrically engage the arcuate resistance track 19 upon the wafer 18 when the cover is in position.

The contact element 53 is secured to the gear 40 by placing the semi-circular edge 54 in engagement with the semi-cylindrical wall 51 of the projection and then forcing the two projections 55 downwardly to slip over and bite into the radially inwardly extending walls 52 terminating the cylindrical wall 51. The dimensions of the wall 51 and the edge 54 and the relative positions of the walls 52 and the projections 55 are such that this engagemeut between the gear 40 and the contact member 53 is a tight interference fit which enables the contact element to be forceably slipped over the projection on the gear to securely mount it in position.

It will be understood that there is a direct relationship between the angular extent of the arcuate resistance track 19, the arcuate slot 38 and the arc subtended by the toothed periphery of the gear 40.

Once the contact member 53 has been secured upon the gear 40, the gear 40 mounted upon its spindle 36 and the shaft 24 placed in position and resiliently biased into sealing engagement with the O-ring 27 by means of the block 30, the cover 15 may be simply placed upon the housing 10 and cemented in position by means of a suitable adhesive. This final operation will have the effect of hermetically sealing the variable resistor or potentiometer.

The simplicity in construction, assembly and operation of the device provides for an economical and eflicient manufacturing process and provides for precision of operation and for a reduced deterioration over prolonged use. The resilient relationship between the gear 40 and the worm gear 25 provides for a virtual elimination of backlash and provides further for a positive drive to the rotatable contact element 53 when the gear 40 is being rotated between its two extreme limits of movement.

A preferred embodiment of the invention has been described with particular reference to the accompanying drawings but it is to be understood that minor modifications of the arrangement and construction of the present invention are contemplated within the scope of the appended claims.

What -I claim as my invention is:

1. A gear drive for a variable resistor comprising an input shaft carrying a worm gear and mounted for unlimited -rotation in both directions, a spur gear in drivable engagement with the worm gear and mounted for rotation of less than 360 about an axis at to the input shaft, stop means to limit the rotation of the spur gear to less than 360, gear teeth on the periphery of the spur gear over a circumferential distance subtending an angle of less than 360 and equal to the angle through which the spur gear can rotate between said stop means, means providing for a radially inward resilient displacement of a portion of the toothed periphery of the spur gear under continued rotation of the worm gear after the spur gear has reached a limiting position.

2. A gear drive as claimed in claim 1 wherein a housing is provided to enclose the input shaft and the spur gear, the input shaft having a collar adjacent one end, an O-ring about the shaft and on that side of the collar adjacent said one end, the housing having a through bore to receive said one end and means to urge the shaft into said 'bore to compress the O-ring between the collar and the housing around the bore so as to seal the shaft in the bore.

3. A gear drive as claimed in claim 2 wherein the means urging the said one end of the shaft into the bore comprises a block of resilient material interposed between the opposite end of the shaft and another part of the housing.

4. A gear drive as claimed in claim 1 wherein the spur gear is provided with an axially extending projection defined by a first surface which is a segment of a cylinder and by a second surface which is chordal to said segment of a cylinder, a metallic contact member having a correspondingly shaped opening which is an interference fit on said projection forceably' applied over said projection to be carried by and rotate with the spur gear.

5. A gear drive as claimed in claim 4 wherein the correspondingly shaped opening in the contact member has small sharp projections associated with the edge engaging With the chordal surface of the projection on the spur gear.

6. A gear drive for a variable resistor comprising an input shaft carrying a worm gear and mounted for unlimited rotation in both directions, a spur gear in drivable engagement with the worm gear and mounted for rotation of less than 360 about an axis at to the input shaft, stop means to limit the rotation of the spur gear to less than 360", the periphery of the spur gear being interrupted by an inwardly extending, radially oriented recess merging with an arcuate slot concentric with the gears periphery to define a pair of externally toothed limbs extending towards one another and separated by the radial recess, each limb being radially displaceable inwardly when the worm gear is rotated after the spur gear has reached its limiting positions.

7. A gear drive as claimed in claim 6 wherein the stop means limiting the rotation of the spur gear will arrest the spur gear in a position such that one of the externally toothed limbs will 'be in engagement with the worm gear on the input shaft.

8. A gear drive as claimed in claim 7 wherein the input shaft and its worm gear are relatively rigid and non-resilient and the spur gear is formed of a material that is inherently resilient.

9. A gear drive as claimed in claim 7 wherein the input shaft and its worm gear are formed of metal and the spur gear is formed of a resilient plastic composition.

References Cited UNITED STATES PATENTS 3,208,024 9/1965 Enos et al 338-174 X 3,235,827 2/1966 Baker 338-474 X 3,242,452 3/ 1966 Grundwald et al 338174 DONLEY J. STOCKlN G, Primary Examiner. L. H. GERIN, Assistant Examiner.

U.S. Cl. X.R. 7410.85, 411, 425, 435; 338-174 

